1. Field of the Invention
The present invention relates to an exposure apparatus. The present invention is suitable, for example, for an illumination optical system for an exposure apparatus using the extreme ultraviolet (“EUV”) light having a wavelength from 10 to 15 nm for the exposure light.
2. Description of the Related Art
A conventional EUV exposure apparatus uses the EUV light having a wavelength from 10 to 15 nm, and requires an illumination optical system configured to efficiently and uniformly illuminate an illumination area on an original (reticle).
A dioptric optical system that uses a lens is not practical since a material's absorption of the light significantly increases in the EUV region. Therefore, the EUV exposure apparatus uses a catoptric optical system.
Japanese Patent Laid-Open No. (“JP”) 11-312638, Japanese Domestic Publication No. (“JD”) 2004-510340, JP 2003-045774 disclose such an illumination optical system for the EUV exposure apparatus.
JP 11-312638 discloses an illumination optical system that uses a first fly-eye mirror and a second fly-eye mirror which have arc contours, and is configured to illuminate an arc area. The first and second fly-eye mirrors are arranged so that a plurality of light source images can be formed on the second fly-eye mirror, and the two fly-eye mirrors serve as one integrator.
JD 2004-510340 discloses an illumination optical system that includes a first fly-eye mirror and a second fly-eye mirror which have rectangular contours, and at least one high-incidence type field mirror configured to illuminate an arc area. The first and second fly-eye mirrors are arranged so that a plurality of light source images can be formed on the second fly-eye mirror, and the two fly-eye mirrors serve as one integrator.
JP 2003-045774 discloses an illumination optical system in which a first corrugate plate integrator (which is an integrator in which a multiplicity of cylindrical surfaces are arranged in parallel) and a first condenser uniformly illuminate a second corrugate plate integrator, and the second corrugate plate integrator and the second condenser illuminate an arc area.
However, these prior art structures have the following problems in efficiently and uniformly illuminating the illumination area on the original (reticle):
The illumination optical system disclosed in JP 11-312638 has a difficulty in manufacturing an arc-shaped fly-eye mirror.
The illumination optical system disclosed in JD 2004-510340 has a problem with a distortion of an effective light source distribution and a degradation of an imaging characteristic because the rectangular illumination area is distorted by the high-incidence type field mirror.
The illumination optical system disclosed in JP 2003-045774 eliminates the unevenness of the effective light source using two corrugate plate integrators, but has a problem of a decrease of the illumination efficiency due to lack of a field mirror when a light source has a large etendue.